Sanaatanism (Sanaatan Dharm), popularly called as ‘Hinduism’, is considered the oldest surviving religion in the world. There are number of holy scriptures, majorly written by the sage/prophet, Ved Vyas.
The religion doesn’t forbids non-vegetarianism (meat-eating) but it strictly restricts the slaughter and consumption of specific animals like cows/bulls, buffaloes and one-hoofed animals (includes horses, donkeys and zebras) as mentioned in the Veds (holy scriptures).
Here is what this religion have to say on ‘meat-eating’ and ‘non-vegetarianism’:
Ved – Rigved (Chapter 1, Verse 164.40):
Text; सू॒य॒व॒साद्भग॑वती॒ हि भू॒या अथो॑ व॒यं भग॑वन्तः स्याम। अ॒द्धि तृण॑मघ्न्ये विश्व॒दानीं॒ पिब॑ शु॒द्धमु॑द॒कमा॒चर॑न्ती ॥
Translation; The Aghnya cows – which are not to be killed under any circumstances– may keep themselves healthy by use of pure water and green grass, so that we may be endowed with virtues, knowledge and wealth.
Ved – Rigved (Chapter 7, Verse 56.17):
Text; द॒श॒स्यन्तो॑ नो म॒रुतो॑ मृळन्तु वरिव॒स्यन्तो॒ रोद॑सी सु॒मेके॑। आ॒रे गो॒हा नृ॒हा व॒धो वो॑ अस्तु सु॒म्नेभि॑र॒स्मे व॑सवो नमध्वम् ॥१७॥
Translation; Cow slaughter has been declared a heinous crime equivalent to human murder and it has been said that those who commits this crime should be punished.
Ved – Rigved (Chapter 8, Verse 101.15)
Text; मा॒ता रु॒द्राणां॑ दुहि॒ता वसू॑नां॒ स्वसा॑दि॒त्याना॑म॒मृत॑स्य॒ नाभि॑: । प्र नु वो॑चं चिकि॒तुषे॒ जना॑य॒ मा गामना॑गा॒मदि॑तिं वधिष्ट ॥
माता रुद्राणां दुहिता वसूनां स्वसादित्यानाममृतस्य नाभिः । प्र नु वोचं चिकितुषे जनाय मा गामनागामदितिं वधिष्ट ॥
Translation; “(She who is) the mother of the Rudras, the daughter of the Vasus, the sister of the Adityas, the homeof ambrosia– I have spoken to men of understqanding– kill not her, the sinless inviolate cow.”
Ved – Yajurved (Chapter 13,Verse 48):
Text; इ॒मं मा हि॑ꣳसी॒रेक॑शफं प॒शुं क॑निक्र॒दं वा॒जिनं॒ वाजि॑नेषु। गौ॒रमा॑र॒ण्यमनु॑ ते दिशामि॒ तेन॑ चिन्वा॒नस्त॒न्वो᳕ निषी॑द। गौ॒रं ते॒ शुगृ॑च्छतु॒ यं द्वि॒ष्मस्तं ते॒ शुगृ॑च्छतु ॥४८ ॥
Translation; Do not slaughter this one hoofed animal that neighs and who goes with a speed faster than most of the animals.
Ved – Yajurved (Chapter 13, Verse 49):
Text; इ॒मꣳ सा॑ह॒स्रꣳ श॒तधा॑र॒मुत्सं॑ व्य॒च्यमा॑नꣳ सरि॒रस्य॒ मध्ये॑। घृ॒तं दुहा॑ना॒मदि॑तिं॒ जना॒याग्ने॒ मा हि॑ꣳसीः पर॒मे व्यो॑मन्। ग॒व॒यमा॑र॒ण्यमनु॑ ते दिशामि॒ तेन॑ चिन्वा॒नस्त॒न्वो᳕ निषी॑द। ग॒व॒यं ते॒ शुगृ॑च्छतु॒ यं द्वि॒ष्मस्तं ते॒ शुगृ॑च्छतु ॥४९ ॥
Translation; Do not kill cows and bulls who always deserve to be protected.
Many people don’t consider Manusmriti text a part of religion. Considering some do, here is the reference…
Manusmriti (Chapter 5,Verse 31 & Verse 32):
31. ‘The consumption of meat (is befitting) for sacrifices,’ that is declared to be a rule made by the gods; but to persist (in using it) on other (occasions) is said to be a proceeding worthy of Rakshasas.
32. He who eats meat, when he honours the gods and manes, commits no sin, whether he has bought it, or himself has killed (the animal), or has received it as a present from others.